From: Ben Giddings <bg-rubytalk@...>
Date: 2005-03-24T08:55:14+09:00
Subject: Re: Credit Card Verification as an exercise

Florian Gross wrote:
> case card_type
>   when 'visa' then
>     [13, 16].include?(digit_length) and number[0, 1] == "4"
>   when 'mastercard' then
>     digit_length == 16 and ("51" .. "55").include?(number[0, 2])
>   when 'amex' then
>     digit_length == 15 and %w(34 37).include?(number[0, 2])
>   when 'discover' then
>     digit_length == 16 and number[0, 4] == "6011"
> end
> 

Actually, you don't need the "then"s either (and you should probably 
have an else, even though nil is "untrue" as well)

case card_type
when 'visa'
   [13, 16].include?(digit_length) and number[0] == ?4
when 'mastercard'
   digit_length == 16 and ("51" .. "55").include?(number[0, 2])
when 'amex'
   digit_length == 15 and %w(34 37).include?(number[0, 2])
when 'discover'
   digit_length == 16 and number[0, 4] == "6011"
else
   false
end

Ben